(1) Field of the Invention
The present invention relates to a technique for distributing digital contents.
(2) Description of the Related Art
Recording media such as DVDs on which digital works such as movies and music are recorded are becoming widespread. Recording media such as DVDs have a large amount of information digitally recorded thereon, and therefore can be used semipermanently without deterioration.
A large market has been built by the evolution of businesses that use such recording media to sell and/or rent out recording media on which movies and music are recorded. Prevention of illegal use of digital works recorded on recording media is crucial for such businesses.
Japanese patent No. 3073590 discloses an electronic data protection system that aims to prevent illegal use of computer software, electronic publications and the like stored on recording media.
This electronic data protection system protects electronic data stored on a recording medium that is used in a user apparatus, based on usage permission from an apparatus held by a usage permitting party. The recording apparatus stores a medium unique number that uniquely specifies the encrypted electronic data and the recording medium. The usage permitting apparatus includes a decryption key for decrypting encrypted electronic data stored on the recording medium, a permission information generation unit that, based on the medium unique number stored on the recording medium, encrypts the electronic data decryption key and generates permission information, and a writing unit that writes the permission information generated by the permission information generation unit to the recording medium. The user apparatus includes a reading unit that reads the permission information, the encrypted electronic data and the medium unique number from the recording medium, a decryption key generation unit that, based on the medium unique number, decrypts the permission information and generates the electronic data decryption key, and an electronic data decryption unit that, based on the electronic data decryption key generated by the decryption key generation unit, decrypts the encrypted electronic data.
According to such a structure, an electronic data protection system can be obtained that enables the user apparatus to use only encrypted electronic data that is stored on a legitimate storage medium and whose usage has been permitted by the usage permitting apparatus.
Furthermore, the abstract published in International Publication Number WO 00/63860 (International publication date: 26 Oct. 2000, International application number: PCT/US00/10414) discloses the following technique.
A system, method and article of manufacture is provided for tracking the distribution of content electronically. First, an electronic storage medium tracking identifier is incorporated onto an electronic storage medium and stored on a database. Next, a package tracking identifier is situated onto a package in which the electronic storage medium is stored. The electronic storage medium is then tracked while being shipped between various entities using the tracking identifier on the package. Further, the electronic storage medium may be identified using the tracking identifier on the electronic storage medium in order to afford authorized use of the information contained on the electronic storage medium.
Since various techniques such as those described above have come to enable prevention of illegal usage of contents written to recording media, businesses that rent and/or sell such recording media are expanding.
However, recently sub-content that relates to content recorded on a recording medium is being distributed in a manner other than on a recording medium. An example of sub-content is a preview for the sequel of a movie recorded on the recording medium. The preview is distributed to users via the Internet or the like.
However, while the above-described techniques for preventing illegal usage of content can prevent illegal usage of the content written to the recording medium, there is a problem that such techniques cannot prevent illegal usage of sub-content that relates to the content written to the recording medium that are distributed via another distribution path.